Soo.. the other day I read that the Alpha Centauri system might have several exoplanets apart from Proxima b.. so I looked for info about the Starshot project and found out that the team launched in July a 3.5 x 3.5cm satellite weighing 4 grams.. this encourages me to believe that the project can actually be achievable.. what do you guys think? do you think that a faster interstellar travel system will be developed even sooner?

I decided to make a video on this exciting topic and I would like to share it with you guys: https://youtu.be/jF2juqeDa-EI honestly can't wait 44 years for receiving the first images of Proxima b, I would be 70 years old. There must be another way of getting there sooner.

Currently my bet is on fusion rockets and true life extension. I want to live to visit another star system myself, in person, one day. It's not a sure bet by any stretch, but if I can keep breathing long enough to turn into a transhuman cyborg I just might make it.Fusion rockets because, if FTL is possible, the Fermi Paradox implies it sure as hell ain't easy, so in all likelihood we're going to be doing our first interstellar colonization without it; and ion engines and what I call "space propellers" (Cannae, Quantum Vacuum, and EM drives) are way too slow for my tastes.

ᴩʀoʙʟᴇᴍᴇᴄɪᴜᴍ﹖Formerly known as "parameciumkid." Still playing on Intel HD Graphics 4000 ^^ My computer turns 5 this Summer.

Source of the post do you think that a faster interstellar travel system will be developed even sooner?

For an unmanned probe? Probably not. For people? No, with virtually zero doubt.

There are many ideas for how to achieve interstellar travel, ranging from plausible but difficult engineering-wise (e.g. an antimatter rocket), to outright impossible (e.g. EM drive or Alcubierre drive.) Out of all of them, a light reflector like Project Starshot has the fewest question marks in terms of fundamental physics and is also the closest method to being achievable with current technology.

A photon reflector is the most attractive method because photons allow the greatest possible transfer of momentum per unit mass-energy (a photon's momentum is its energy). Furthermore, each photon reflected provides twice the momentum transfer compared to shooting it out the back (as in the photon rocket), although this does break down at relativistic speeds due to the Doppler effect.

But the greatest advantage for the light reflector is that the probe does not need to carry its own fuel with it. The impulse is supplied from Earth. Therefore instead of being constrained by the rocket equation which demands a huge fraction of the rocket's rest mass be consumed to achieve relativistic speeds, we're only limited by how much power a laser can supply to the probe without destroying it, and the mass of the probe.

The greatest disadvantage to the light reflector? It can't slow down at the destination. This isn't a method for getting people to the stars, it's a method of getting a very lightweight probe there and getting the data back within the lifetime of the people involved in the project. It's an amazing idea because for all the apparent difficulties, when we do the math, it actually appears to be achievable if humanity chooses to invest in it. The greatest investment is in the infrastructure, and then once that is in place the cost of launching the probes is very cheap compared to any other method of travel.

I think one last challenge to Project Starshot specifically is that it must justify the expense with the probability of success and quality of data brought back compared to what we can learn from Earth-based astronomy, and projections for how telescopes and observing techniques advance in the next 20-40 years. Surely nothing is better than buzzing a probe directly by the target planet and sending back the photos and other data, but we're still getting better and better about what we can learn about exoplanets without having to actually go there.

For anyone interested in learning more about Starshot from the people directly involved in the project, this CfA lecture is a nice watch:

That was the very first question to come to my mind when I first heard the idea, and one of the members of the audience also asks it at 1:03:50 in the Q&A. I recommend hearing the response in the video since he does a pretty good job explaining what factors into the precision required and how it is achievable, but in short the surprising answer is yes! Probably the best way is to have a small laser on the probe to act as a photon rocket to do midcourse corrections. If you also combine this onboard guidance with launching several probes at once at the target, you can be pretty much guaranteed to get at least one good flyby.

The swarm method also helps solve some of the other potential sources of failure like debris strikes.

Source of the post Debris shouldn't be a problem until arriving at the Centauri system, perhaps. If any probes are lost there, that will be valuable data.

Counter-intuitively it is the cruise through interstellar space that poses the greater risk to the probe. Interstellar space is more empty, but there is a whole lot of it between the stars. At 0.2c even grains of interstellar dust striking the craft would cause damage. This is one aspect of the project that they did some very rigorous work on to figure out the extent of the damage caused to different materials, and it's definitely not negligible, though it can be solved with some clever techniques in the probe design. For example, folding the sail up when not operating during the cruise phase so that it has a small cross section to the flight path, and then protect that cross section with another layer as a shield.

midtskogen wrote:

Source of the post Another question that comes to mind, how will the probes be able to transmit back the data with such a small sender? The inverse square relationship must hurt badly at Proxima Centauri.

The trick here is to use the sail itself as an antenna to transmit the data back. The probe has a small mass, but a large surface area with which to direct the transmission (which does obey the inverse square law, but with a very small divergence angle), and this may be powered by just a 1W laser.

Source of the post Debris shouldn't be a problem until arriving at the Centauri system, perhaps. If any probes are lost there, that will be valuable data.

Counter-intuitively it is the cruise through interstellar space that poses the greater risk to the probe. Interstellar space is more empty, but there is a whole lot of it between the stars. At 0.2c even grains of interstellar dust striking the craft would cause damage. This is one aspect of the project that they did some very rigorous work on to figure out the extent of the damage caused to different materials, and it's definitely not negligible, though it can be solved with some clever techniques in the probe design. For example, folding the sail up when not operating during the cruise phase so that it has a small cross section to the flight path, and then protect that cross section with another layer as a shield.

I'd imagine that the machinery required to fold up the sail would add a lot to the mass of the probe. What about making the sail exceedingly weak and brittle? Then, if an interstellar dust speck hits the solar sail, it only punches a small hole in it.But whenever this happens, the probe will still be knocked into a spin. Sounds like a job for that course-adjustment laser.

Source of the post What about making the sail exceedingly weak and brittle? Then, if an interstellar dust speck hits the solar sail, it only punches a small hole in it.

The sail is already assumed very thin, and "brittleness" doesn't really apply when it comes to hypervelocity impacts. The impactor immediately vaporizes along with a portion of the target. For the specifications of the probes imagined in this project, this basically accumulates damage in the form of small pits in the surface.

Mr. Missed Her wrote:

Source of the post But whenever this happens, the probe will still be knocked into a spin. Sounds like a job for that course-adjustment laser.

Good thinking! Let's go through the math. Angular momentum is [math]L=I\omega, and [math]\omega = 2\pi f where [math]f is the rotational frequency. We'll let the moment of inertia of the probe be of order ~MR2. Finally, the maximum angular momentum that can be transferred from an impacting grain is mvR.

Solve for the rotational frequency,

[math]f = \frac{\omega}{2\pi} = \frac{L}{2\pi I} = \frac{mv}{2\pi MR}

Let's let the grain have mass m=10^-16kg, the probe have velocity v=0.2c, probe mass M=10g, and radius R=10cm. Then the fastest possible rotation rate resulting from one strike is about 10-6 Hz, or about half a rotation per week.

Can a 1W laser take care of this? That is, how long would it take the torque from a 1W laser to cancel the angular momentum gained from this debris strike?

Torque is the change in angular momentum with time. The momentum of a single photon is E/c, so the rate of linear momentum transfer is P/c where P is the power of the laser. The maximum angular momentum this can provide is to fire it tangentially from the edge of the probe (i.e. the distance we earlier called R). Therefore the change in angular momentum supplied by the laser over a period [math]\Delta t is [math]\frac{RP}{c}\Delta t.

Set this equal to the angular momentum given by the dust grain (Rmv), and solve for the time interval, and we get the satisfyingly simple result:

[math]\Delta t = \frac{mvc}{P}

Again let m=10^-16kg, v=0.2c, and P=1W, and this turns out to be a mere 2 seconds!

In other words, the laser can easily take care of any net spin resulting from hypervelocity impacts along the way.

Watsisname, WOW, amazing explanation as always. I was going to answer that but it's much more helpfull when you give an order of magnitud crunching some numbers. A puny spin rate indeed.

Besides that I would like to remind you all that there is plenty of information in the oficial webpage of the project.In the Challenges section they have identified 29 important issues to solve for this mission to be accomplished. There is a little forum for each challenge where people have asked very intelligent questions, in my opinion, and some interesting ideas have been proposed.

midtskogen wrote:

Source of the post Getting within photography range of proxima centuari b will require extreme precision. Can the really aim with such precision? Not to mention getting the timing right?

In short,It is expected that in the 20 years until launch Proxima B gets directly imaged and precission ephemerids are calculated that could make the spacecraft come closer than 1 AU from the planet. This seems a lot of distance still but the project heavily relies on the incremental nature of it. Many spacecrafts can be lunched (since the costs are going to be insignificant compared to current car-sized spacecrafts) with tiny differences in the angle of ejection as to make some of them arrive much more closer than 1 AU to the planet. Some might even crash. Even with that another idea is to have the first nanosails to triangulate the position of the planet with high accuracy and beam the information to a year-appart second wave of nanosails that could maybe make small corrections using the micro-thrusters.

If a planet-to-nanocraft distance of 1 AU and a velocity of 0.2c are assumed, an angular rate of 80 arcsec/s for the slew manouver is needed. This could very easily be acomplished using electrodynamic theters attached to the structure of the sail or the mini-thrusters mentioned before. Extremely efficient image compression and smart feature detection algorithms would be crucial.Taking all of this into account (blurring, distance, etc...) a 40km per pixel image resolution could be accomplished. Using the mini-thrusters the pointing precission would be of below 0.1 arcsecs.

I've taken photoshop to resize images of Earth, the Moon and Europe to match those 40 km/pxl resolution.

As you can see the expected resolution when taking into account the blur because of the errors in pointing around 1 AU distance is enough to show continents, even mountain ranges (look at the alps in Europe), large bodies of water, cloud patterns etc... Is enough to see detail also in an object the size of the Moon. You can see the lunar mare and even the ejecta streaks of the tycho impact crater.Europe has been cleaned of clouds in that image so maybe some features would be hidden.Consider also that Proxima B is a little bigger than the Earth so even if the detail is the same you would see more surface features in the image.

midtskogen wrote:

Source of the post how will the probes be able to transmit back the data with such a small sender? The inverse square relationship must hurt badly at Proxima Centauri.

In short,The idea is to transmit the images using a 1W laser onboard. The sail would be used to focus the laser communication signal by shaping the sail into a Fresnel lens that would create a diffraction limit spot size on Earth of 1 km. To receive the weak signal the same laser beamer array used to lunch the probes would be reconfigured to a receiver mode. Current technology have demonstrated that it is possible to detect single photons emitted by lasers from very large distances. The current record holder is the LADEE Laser Communication system, which was able to operate from lunar distances. The current performance is of order 2 bits per photon, so a lot of redundancy in the information sent should be considered as to complete the information from the lost photons at arrival on Earth. It has been estimated that using the laser beamer as a phased array telescope would offer a sufficient collecting area to receive the signal from Proxima Centauri. Other solution contemplated are using a chain of communication relay probes launched in succession as to transmit the signal step by step across the 4 light years between both stellar systems.

Source of the post if an interstellar dust speck hits the solar sail, it only punches a small hole in it.But whenever this happens, the probe will still be knocked into a spin. Sounds like a job for that course-adjustment laser.

Interplanetary dust around the stellar systems is way more frequent than interstellar dust. The nanosail would traverse a few hundreds of AU at most in the denser interplanetary medium so the danger is not so high. Nothing is known about dust in the vicinity of Proxima Centauri (besides maybe some estimates based on this) but a lot is known on the dust in our Solar system. Thankfully Proxima Centauri is above the ecliptic plane from the Sun so the cruise through the dust of the Solar system would be much shorter. Also if the 45º inclination of the asteroid belts around Proxima centauri is true then we should expect also that the dust is accumulated in a plane that is not aligned with Sol and therefore the journey across this medium is also short at the arrival.

The idea of using the laser array on Earth to clear the way some AUs of the first part of the way has also been discussed. Maybe in that way we could peer through the zodiacal dust denser part minutes before the nanosail is lunched.

For interstellar dust each square centimeter of the frontal cross-sectional area of the nanosail would encounter about 1,000 impacts from dust particles of size 0.1 micron and larger. However, there is only a 10% probability of a collision with a 1 micron particle, and a negligible probability of impact with much larger particles. So for 10 nanosails 1 could be lost due to a large impact, thus not comprimising the mission. The rest of the sails would probably be hitted by smaller 0.1 micron objects so this is important. A 0.1 micron dust particle moving at 20% of the speed of light would penetrate and melt the StarChip to a depth of 0.4 mm. Traveling with the nanocraft’s edge facing parallel to the velocity vector would reduce the cross section to 0.1 cm2, for a 10 cm StarChip with a 0.1 mm thickness. A protective coating of beryllium copper could be added to the leading edge of the StarChip, as a sacrificial layer for additional protection from dust impacts and erosion. It could even be elongated to further minimize the cross-section (the sail folded like an arrow).

Also as Watsisname has noted, the momentum kick from 0.1 micron dust particles is small, and its effect on the nanocraft’s trajectory might be compensated for by photon thrusters.

As for charged particles it has been speculated that maybe those could be defelcted using a magnetic field or electrically charging the sail. The problem is tu ensure that the galactic magnetic field does not impose deviations in the path of the spacecraft. In general the erosion due to electrons and protons can be handled with a protective coating over the entire sail. The 18MeV protons would travel several millimeters into the target before stopping. A protective layer sufficient to stop 18 MeV protons would be required to avoid damage to the electronics by proton implantation. The net loss of mass from the forward-facing surface due to sputtering would only amount to a few monolayers. Helium nuclei carry 72 MeV and are 10% as numerous as single protons. Hits by CNO group nuclei carry 200-300 MeV and are ~0.1% as common, and hits by iron nuclei carry ~1GeV of energy and are ~0.01% as common so the risk of damage is low and only a few nanosails would probably be lost because of this.

Source of the post 40 km resolution from 1 AU - how can such a small probe carry a camera capable of that?

Again this is in part adressed in their official website (I'm also skeptic of this incredible resolution but ignorant as to the proposed revolutionary techniques so...).They state that:

"Sub-gram-scale 2 megapixel cameras are currently widely available at very low costs. The trend has been a doubling of pixels for the same mass every two years. It is anticipated that these devices will continue this trend for some time. Advances in planar Fourier capture array cameras should make it possible to eliminate the need for focusing optics in the cameras. Advances in Fresnel lens imaging and planar Fourier capture array cameras should make it possible to build focusing optics in the cameras light enough to be used in the mission, or eliminate the need for focusing optics altogether."

"Using a 4-meter-scale camera array at a distance of 1 AU would provide image resolution of order 40km, assuming visible spectrum imaging. The resolution scale could be improved by closer approaches of less than 1 AU."

I'm sceptical. If this is imminent technology, why hasn't anyone built a prototype as a proof of concept? It would be a useful thing even on Earth. Also, even though there has been massive technological advances recently, largely due to mobile phone cameras, that technology wasn't made to endure decades in space. This sounds like hand waving to me.